Andrew Forrest has some of the world's biggest companies in his sights. The iron ore magnate, fresh from celebrating the opening of Fortescue Metals Group's Hamersley rail line in the Pilbara, is preparing for the public launch of what he says is his biggest challenge.

Over the next decade, Mr Forrest wants to eradicate what he calls "one of the oldest, and certainly ugliest, trades in human history" - forced labour.

To help achieve that, he gave up a cherished executive role at Fortescue in June last year to make time for charitable causes, with new anti-slavery foundation Walk Free chief among them.

At the time there was market speculation that Mr Forrest had handed over the top role at Fortescue for fear of losing a long battle with the Australian Securities and Investments Commission. But Mr Forrest rejects that outright.

"I'd planned the handover of the chief executive-ship for no less than three years, and it was always about what was best for the company, knowing I must balance both philanthropic and business interests," he said.

Since founding the Australian Children's Trust in 2001, the Forrest family has donated more than $US260 million, according to its annual report. About $80 million of that came in 2007, when Mr Forrest donated a big tranche of Fortescue shares, along with options in Poseidon Nickel. It was the largest philanthropic donation in Australian history.

The Children's Trust is best known for establishing GenerationOne and its sister organisation, the Australian Employment Covenant, which work to end the gulf between indigenous and non-indigenous Australians through employment programs.

But both now have other high-profile backers, including James Packer, Kerry Stokes and Lindsay Fox, and Mr Forrest says stepping down from Fortescue was something he "had to do" to concentrate on Walk Free and its anti-slavery campaign.

"There are business people - none which I've met in Australia - who consider the use of forced labour to be good business. And we have to change their mindset and change it rapidly," Mr Forrest said.

This year the International Labour Organisation estimated that 21 million people in the world live in conditions of forced labour.

While institutional slavery is now comparatively rare, it still persists in nations such as Mauritania. But forced labour exists in many other forms - from the plight of Filipino domestic staff in parts of Asia and the Middle East, to Uzbekistan where more than a million adults and children are forced each year to harvest cotton, to child labour in West Africa's coffee plantations. In 2005, the ILO estimated that forced labour generated $US32 billion in profits a year.

After a "soft launch"earlier this year, in August Walk Free claimed victory in one of its first campaigns, helping local activists pressure the Philippine Senate to ratify an ILO convention covering the treatment of domestic workers. In October, a Walk Free campaign helped push international fashion chain Zara to agree to abandon the use of Uzbek cotton.

Walk Free is also developing a global index to measure the impact of slavery and what governments are doing to tackle it. And it will soon launch a global fund to back other anti-slavery groups and help give governments and activists the resources to tackle the problem.

The last pillar of the strategy has Mr Forrest's direct involvement.

Fortescue asked its suppliers and contractors to certify they and their direct supply chains were free of slavery and forced labour.

In a recent letter seeking support for Walk Free to other business and political leaders, Mr Forrest said "with barely a degree of separation, we discovered aspects of slavery in both our upstream and downstream commercial relationships".

Those companies reacted quickly, he said, moving to eliminate any aspect of slavery in their own supply chains.

Walk Free's pressures others to do the same. If they won't, Mr Forrest is happy to ring their boss himself, personally lobbying directors and executives to lend weight to public campaigns waged by other non-government organisations.

"In the business world part of the thrust and parry, according to a lot of chief executives, is pressure from NGOs. It's taken as part of business and is often dealt with in quite a dismissive way," he said.

But a call from the chairman of the fourth biggest iron ore miner in the world is treated differently.

"We're able to reach into the most influential families of the world and discuss with them candidly that the world has a rapidly growing problem - the dark side of globalisation is forced labour and slavery. And it's not just happening in the small businesses in India, or in the human traffic out of Nepal, it's happening under our noses where some organisations allow their supply chains and contractors to undercut their rivals using forced labour and slavery."

Though he is yet ready to name Walk Free's targets, Mr Forrest says they include big names in the electronics and construction, as well as commodity trading houses.

The reporter recently travelled to the Pilbara with Mr Forrest as a guest of Fortescue Metals Group.